1. Technical Field
The present disclosure relates to an epitaxial base, a method for making the epitaxial base and an epitaxial structure.
2. Description of Related Art
Light emitting devices such as light emitting diodes (LEDs) based upon group III-V nitride semiconductors such as gallium nitride (GaN) have been used in many fields.
Since wide GaN substrates cannot be produced, the LEDs have been produced on a heteroepitaxial base such as sapphire. The use of sapphire substrate is problematic due to lattice mismatches and thermal expansion mismatches between the GaN and the sapphire substrates. One consequence of the thermal expansion mismatches is straining the GaN/sapphire substrate structure, which leads to cracking of the GaN/sapphire substrate and difficulty in fabricating devices with small feature sizes. A solution to cure the thermal expansion mismatches is to form a plurality of grooves on the surface of the sapphire substrate by lithography or by etching before growing the GaN layer. However, both the processes of lithography and etching are complex, high in cost, and may contaminate the sapphire substrate.
What is needed, therefore, is to provide a method for growing an epitaxial structure that overcomes the problems as discussed above.